1. Field of Invention
This invention relates to metal keyway forms for use in the laying of concrete. In particular, this invention relates to an adjustable support which is securable to metal decking for the support of metal keyway forms.
2. Prior Art
Concrete is used for flooring in most major buildings because of its strength, durability and reliability. However, because concrete tends to expand and contract depending on the temperature, concrete slabs frequently crack once they have dried. In addition to cracking, concrete tends to buckle and rise at the point of any fractures caused by the cracking of concrete slabs.
To allow for expansion and contraction, while at the same time preventing the vertical displacement of the concrete, metal divider strips adapted to form a keyway between two adjacent concrete slabs have been developed. Many different forms of these sheet metal keyways have been provided including, for example, those disclosed in U.S. Pat. Nos. 4,516,875, 4,455,104, 4,443,981, 4,411,404, 4,012,024, 3,770,237, 3,628,764, 3,561,721, 3,288,042 and 3,057,269. Each of these patents discloses a slightly different keyway forming member or some improvement or modification to a keyway form.
These keyway forms have been used exclusively to form keyways in concrete slab on the ground or earth. In setting up the keyway forms before pouring the concrete, vertical stakes are driven into the ground or subground and arranged with their upper ends near the proposed height of the concrete slab. These stakes are provided with some means of attachment to the keyway forms to hold the forms at a preset height. These means for attachment of the stake to the keyway form have also been the subject of numerous patents including for example, U.S Pat. Nos. 4,516,875, 4,455,104, 4,411,404, 4,012,024, 3,784,313, 3,770,237, 3,628,764, 3,561,721, 3,401,612, 3,288,042 and 3,057,269.
While these patents provide a method for forming a metal keyway in concrete poured on the ground, none disclose a keyway form for use in buildings where metal decking is used as the support for the concrete floor. Conventionally, three methods have been used for forming concrete slabs on metal decking. The first is merely the use of wood, usually in the shape of two-by-fours to establish the area in which the slab is poured. The wood is secured in the location desired on the metal decking and the concrete is poured up against it. Sometimes if a keyway is desired, a second piece of wood is secured against the first piece of wood and the concrete is poured over that portion to create the key. While this somewhat crude method has frequently been used, it is labor intensive and time consuming since after the concrete is poured, all of the wood must be removed which requires the chipping away of concrete from the wood forms. Further, concrete can only be poured on one side of the wood at a time thereby increasing the time necessary for the pouring of the concrete floor.
A second commonly used method does not form a keyway at all, but rather is used merely as an accessory to the screeding of the concrete. This procedure requires the placement of screed chairs or pedestals with piping or wood braces running in the opening of the pedestal. The concrete is poured up to the point of the piping, screeded by using the pipe as a base and allowed to set. The pipe is then removed and reused in other concrete laying operations. While this procedure allows for the efficient screeding of the concrete, it does not form any type of key-joint and it does require a good deal of labor to remove the piping with the excess concrete dried up against it.
The third method for pouring concrete on metal decking requires the use of pre-set concrete forms. See for, example, the screed rails sold by VM Permaban, Inc. A generally I-shaped concrete form is placed on the metal decking in the location required for the concrete slab. The concrete form is carefully located on the decking so that the height of the floor is precisely controlled. Once the concrete form is placed on the decking, it is secured to the decking at a few locations by pouring concrete under the form. The concrete form must then be tapped down to assure that the concrete floor to be poured will be flat and the concrete allowed to set. Only then can the main concrete slab be poured. While these concrete forms can be used for the pouring of concrete slabs on metal decking, they have several significant deficiencies since they are brittle, expensive, and take a significant amount of set up time because of the difficulty in locating them precisely on the floor and the delays caused after the initial pouring of concrete to secure the forms in place.
Therefore it is the object of this invention to provide an easy, inexpensive method of securing a metal keyway form to metal decking.
It is another object of this invention to provide a metal decking support which is adjustable to provide various heights to a metal keyway form.
It is a still further object of this invention to provide an adjustable metal decking support which is inexpensive to produce, and easy to secure to metal decking.
These and other objects and features of the present invention will become apparent to those skilled in the art from a consideration of the following detailed description, drawings and claims. The description along with the accompanying drawings provide a selected example of construction of the device to illustrate the invention.